Noise sound controller

ABSTRACT

A noise sound controller being capable of following a sudden change in a noise period, includes a differential signal calculation means 5 that calculates a differential signal between an output from a sound wave-electric signal converter 2 and an output from an adaptive filtering means 6, a transfer characteristics simulation means 4 that is inserted between the adaptive filtering means 6 and the differential signal calculation means 5, and simulates transfer characteristics of a system from the adaptive filtering means 6 to the differential signal calculation means passing through the electric signal-sound wave converter 3 and the sound wave-electric signal converter 2, a period-detecting unit 7 that detects the noise period of noise from a noise source 1, a period-adjusting unit 8 that varies the period of an output signal from the differential signal calculation means 5 depending upon an amount of change in the noise period, and a period detect/control means (10) that changes filter coefficients of the adaptive filtering mens 6 depending on estimated change in the noise period.

DESCRIPTION

1. Technical Field

The present invention relates to a noise sound controller that erases anoise sound by outputting from a speaker a compensation sound that has aphase opposite to and a sound pressure equal to those of the noise soundthat is detected by a microphone; the noise sound controller beingcapable of following even a sudden change in the frequency of the noisesound.

2. Background Arts

Passive silencer devices such as mufflers have heretofore been used tosuppress the noise sound generated by internal combustion engines,leaving, however, much room for improvement from the standpoint of sizeand silencing characteristics.

To overcome these shortcomings there has been proposed an active noisesound controller that outputs, from a speaker, a compensation sound thathas a phase opposite to and a sound pressure equal to those of a noisesound generated from a noise source, in order to eliminate the noisesound.

However, putting the active noise sound controllers into practical usehas been delayed because of insufficient frequency characteristics orstability thereof.

Owing to the development in recent years of signal processing technologyusing digital circuitry enabling a wide range of frequencies to betreated, however, many practical noise sound controllers have beenproposed (see, for example Japanese Unexamined Patent Publication No.63-311396).

The above publication discloses an active noise sound controller of theso-called two microphones and one speaker type consisting of acombination of a feedforward system and a feedback system, in which anoise sound is detected by a microphone that is installed on theupstream side of a duct to pick up the noise sound from a noise source,and is processed by a signal processing circuit and outputs, from aspeaker installed on the downstream side of the duct, a signal that hasa phase opposite to and a sound pressure equal to those of the noisesound, and the silenced result is detected by a microphone at asilencing point and is fed back.

On the other hand, in order to obtain a silencing effect in a spacewhere the site of the noise source is ambiguous such as in the interiorof an automobile, it is necessary to employ a device having aone-microphone one-speaker constitution using the feedback system onlywithout installing a microphone at the noise source.

In the active noise sound controller constituted by one microphone andone speaker based on a feedback system only, however, the silencingeffect decreases when the noise period of a noise source suddenlychanges since the feedback system has a delay defect that is greaterthan the sound wave transfer characteristics from at least the speakerto the microphone.

In view of the above-mentioned problems, therefore, the object of thepresent invention is to provide a noise period controller that iscapable of following a sudden change in the noise period.

DISCLOSURE OF THE INVENTION

FIG. 1 is a diagram illustrating the first principle and constitution ofthe present invention. In order to solve the above-mentioned problem,the present invention provides a noise sound controller having a soundwave-electric signal converter 2 that detects noise and converts it intoan electric signal, and an electric signal-sound wave converter 3 thatoutputs a compensation sound wave to erase noise, wherein a noise periodcontroller comprises a transfer characteristics simulation means 4, adifferential signal calculation means 5, an adaptive filtering means 6,a period-detecting unit 7, and a period-adjusting unit 8.

The differential signal calculation means 5 calculates a differentialsignal between an output of the sound wave-electric signal converter 2and an output of the adaptive filtering means 6.

The transfer characteristics simulation means 4 is inserted between theadaptive filtering means 6 and the differential signal calculation means5, and simulates the transfer characteristics from the adaptivefiltering means 6 to the differential signal calculation means 5 passingthrough the electric signal-sound wave converter 3 and the soundwave-electric signal converter 2.

The period-detecting unit 7 detects the noise period of the noise source1.

The period-adjusting unit 8 varies the period of an output signal of thedifferential signal calculation means 5 depending upon the amount ofchange of the noise period. Based on the output signal from theperiod-adjusting unit 8 and the output of the sound wave-electric signalconverter 2, the adaptive filtering means 6 calculates a compensationsignal, with which the electric signal-sound wave converter 3 outputs acompensation sound wave. The adaptive filtering means 6 may directlyinput a signal that is obtained by adjusting the period of a noisesignal from the noise source. In this case, the transfer characteristicssimulation means 4 and the differential signal calculation means 5 maybe omitted.

According to the noise period controller shown in FIG. 1, a noise signalis formed from a differential signal that is output by the differentialsignal calculation means 5 based on the output of the transfercharacteristics simulation means 4 and the output of the soundwave-electric signal converter 2; the amplitude and phase are adjustedby the adaptive filtering means 6 that inputs the noise signal, and acompensation sound wave is output from the electric signal-sound waveconverter 3 in response to the compensation signal, thereby cancelingthe noise. Furthermore, the period-detecting unit 7 detects the noiseperiod to monitor a change in the noise period, and the period-adjustingunit 8 adjusts the output signal of the differential signal calculationmeans 5, i.e., adjusts the period of the input signal of the adaptivefiltering means 6 depending on a change in the noise period. Therefore,the period of the compensation sound wave from the electric signal-soundwave converter 3 comes into agreement with the period of noise at thesilencing point. Accordingly, even a sudden change in the noise periodcan be followed.

FIG. 2 is a diagram illustrating the second principle and constitutionof the present invention. In order to solve the above-mentioned problem,the present invention provides a noise sound controller comprising anelectric signal-sound wave converter 3 that erases a noise sound from anoise source 1, a sound wave-electric signal converter 2 that converts,into an electric signal, a residual sound of the noise sound erased bythe sound wave from said electric signal-sound wave converter 3, and anadaptive filtering means 6 that sends a compensation signal for erasingthe noise sound to said electric signal-sound wave converter 3 based ona signal from said sound wave-electric signal converter 2; the noisesound controller further comprising a period detect/control means 10that changes the filtering characteristics of the adaptive filteringmeans 6 depending on an estimated change in the noise period.

The period detect/control means 10 detects the noise period of the noisesource 1, estimates a change in the noise period, and newly setsmultiplication coefficients that have been set in a plurality ofmultipliers included in said adaptive filtering means 6 depending on theestimated change in the noise period.

Moreover, the period detect/control means 10 detects the noise period ofthe noise source 1, estimates a change in the noise period, and movesoutput taps of a plurality of delay units that are included in theadaptive filtering means 6.

Furthermore, the period detect/control means 10 forms vectors of aplurality of dimensions, detects a change in the vectors, estimates thechange thereof, and newly sets the multiplication coefficients of aplurality of multipliers included in the adaptive filtering means 6.

According to the noise sound controller shown in FIG. 2, the noise iserased since a compensation signal of the adaptive filtering means 6that inputs a noise signal is adjusted in amplitude and phase inresponse to a differential signal between a noise from the noise source1 and a sound wave from the speaker 3 having a phase opposite to and asound pressure equal to those of the noise. When the noise periodsuddenly changes, the period detecting means detects a change in thenoise period, estimates the change in the previous noise period bytaking into consideration the transfer characteristics up to a silencingpoint via the electric signal-sound wave converter 3 and the like, andshifts and controls the multiplication coefficients of a plurality ofmultipliers that constitute the adaptive filtering means 6, so that theperiod of a compensation sound wave from the electric signal-sound waveconverter 3 is in agreement with the period of noise at the silencingpoint. Therefore, even a sudden change in the noise period can befollowed.

The same operation is obtained even when the taps of the delay units inthe adaptive filtering means 6 are moved by the period detecting means10.

Moreover, multiplication coefficients of multipliers in the adaptivefiltering means 6 are obtained in the form of vectors by the perioddetecting means 10; the change in the vectors being intimately relatedto the noise period. Therefore, the noise period can be easily estimatedby estimating the change in the vectors, and the period of thecompensation sound wave can be brought into agreement at the silencingpoint by taking the transfer characteristics into consideration despitethe sudden period changes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the first principle and constitution ofthe present invention;

FIG. 2 is a diagram illustrating the second principle and constitutionof the present invention;

FIG. 3 is a diagram illustrating a noise period controller according toa first embodiment of the present invention;

FIG. 4 is a diagram explaining a method of detecting the period by theperiod-detecting unit of FIG. 3;

FIG. 5 is a diagram illustrating the constitution of theperiod-adjusting unit of FIG. 3;

FIG. 6 is a diagram illustrating a relationship of input and outputsignals of the period-adjusting unit of FIG. 5;

FIG. 7 is a diagram illustrating a relationship between the amount ofchange in the period and the calculated amount of control therefor;

FIG. 8 is a diagram explaining the function of the delay amount controlunit;

FIG. 9 is a diagram illustrating a noise period controller according toa second embodiment of the invention;

FIG. 10 is a diagram illustrating a noise period controller according toa third embodiment of the present invention;

FIG. 11 is a diagram illustrating a noise period controller according toa fourth embodiment of the present invention;

FIG. 12 is a diagram illustrating a noise sound controller according toa fifth embodiment of the present invention;

FIG. 13 is a diagram showing the constitution of the perioddetect/control means of FIG. 12;

FIG. 14 is a diagram explaining a method of detecting the period by theperiod detecting unit of FIG. 13;

FIG. 15 is a diagram explaining a method of estimating the amount ofchange in the period;

FIG. 16 is a diagram illustrating the adaptive filtering means of FIG.12;

FIG. 17 is a diagram explaining the shifting of multiplicationcoefficients of a plurality of multipliers that constitute the adaptivefiltering means;

FIG. 18 is a diagram explaining the tap moving of a plurality of delayunits that constitute the adaptive filtering means; and

FIG. 19 is a diagram illustrating a modified example of the perioddetect/control means of FIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention will now be described in conjunction withthe drawings.

FIG. 3 is a diagram illustrating a noise period controller according toa first embodiment of the present invention. The constitution of thisdiagram will now be described. The constitution of this diagramcomprises a noise source 1 such as an engine or a motor of anautomobile, a microphone 2 that traps, near a silencing point, aresidual sound canceling a sound wave propagated from the noise source 1and converts the residual sound into an electric signal, a an errorsignal a speaker 3 that outputs the compensation sound wave to erasenoise near the silencing point, a transfer characteristics simulationmeans 4 that simulates transfer characteristics of a system from theadaptive filtering means 6 to the differential signal calculation means5 passing through the speaker 3 and the microphone 2, a differentialsignal calculation means 5 that calculates a differential signal betweenthe output of the microphone 2 and the output of the transfercharacteristics simulation means 4, an adaptive filtering means 6 thatcalculates a compensation signal based on a calculated result of thedifferential signal calculation means 5 to output a compensation soundwave from the speaker 3, a period-detecting unit 7 that detects thenoise period of the noise source 1, a period-adjusting unit 8 thatvaries the period of an input signal to the adaptive filtering means 6depending upon the amount of noise period change, an amplifier 101 forthe microphone 2, an A/D converter (analog to digital converter) 1 thatdigitizes the output of the amplifier 102 and outputs it to thedifferential signal calculation means 5, a D/A converter (digital toanalog converter) 103 that converts the output of the adaptive filteringmeans 6 into an analog value, and an amplifier 104 that amplifies theoutput of the D/A converter 103 and outputs it to the speaker 3. Theadaptive filtering means 6 may be constituted by a band-pass filter, adelay unit and an amplifier.

Here, the transfer characteristics simulation means 4, differentialsignal calculation means 5, adaptive filtering means 6, period-detectingunit 7, and period-adjusting unit 8 are constituted by DSPs (digitalsignal processors).

FIG. 4 is a diagram explaining a method of detecting the period by theperiod-detecting unit of FIG. 3, wherein the diagram (a) explains amethod of detecting the timing of rotation, such as an engine of anautomobile, which is the noise source 1. A signal of a rectangular waveis input as designated at 1 to the period-detecting unit 7 where aperiod T is found and is output as designated to 2 to theperiod-adjusting unit 8. In the case of an automobile, a sudden changein the noise is caused by a change in the number of revolutions of theengine of the automobile.

The diagram (b) explains the method of detecting the noise waveform byinstalling a microphone near the engine of the automobile in order toobtain a period T of a noise signal from the peaks in the time waveformwhen the timing signals are not obtained as shown in the diagram (a). Inthis signal processing, a rectangular wave is generated when the levelof a noise signal has exceeded a predetermined level and is input to theperiod-detecting unit 7, thereby obtaining the period T in the samemanner as in the diagram (a).

The diagram (c) explains a BPF (band-pass filter) peak detection methodfor finding a noise period T after a noise signal input to themicrophone is digitized. This method comprises a plurality of band-passfilters 1, 2, - - - , n, absolute value units (ABS) connected to theband-pass filters 1, 2, - - - , n, averaging units (LPF) connected tothe absolute value units, and maximum band-detecting units that detectmaximum values of the averaging units, wherein a maximum frequency bandof the noise level is detected and a period of the maximum frequencyband is used as a period of a noise signal.

The diagram (d) explains a method of detecting the period using anadaptive filter comprising a delay unit (delay) that inputs adifferential signal from the differential signal calculation means 5, anadaptive filter (ADF) that inputs the output from the delay unit, anadder unit that obtains a differential signal between the output of theadaptive filter and the input signal and a least-squares processing unit(LMS) that subjects the differential signal of the adder unit to themethod of least squares to determine a coefficient of the adaptivefilter. The period of a noise signal is found from a fixed coefficientof the adaptive filter.

FIG. 5 is a diagram illustrating the constitution of theperiod-adjusting unit of FIG. 3. The period-adjusting unit 8 diagrammedhere includes a delay memory 81 that inputs the differential signal fromthe differential signal calculation means 5, has delay types of a numberof M, and sends an output to the adaptive filtering means 6 from a delaypoint thereof, a delay amount control unit 82 that controls the amountof delay by moving the delay point of the delay memory 81, a periodchanging amount detecting unit 83 that detects the amount of change inthe period based on the period data from the period-detecting unit 7,and a control amount calculation unit 84 that calculates the delaycontrol amount that changes the delay point based on the amount ofchange in the period.

FIG. 6 is a diagram illustrating a relationship of input and outputsignals of the period-adjusting unit of FIG. 5, wherein the diagram (a)shows that the input signal to the delay memory 81 has a period T3 andthe diagram (b) shows that the output signal of the delay memory has aperiod T4.

FIG. 7 is a diagram illustrating a relationship between the amount ofchange in the period and the calculated amount of control therefor. Ifthe period first remains constant and then decreases starting at a givenmoment (t₀), the amount of change in the period is detected by theperiod changing amount detecting unit 83 as represented by 2 in thedrawing. According to the prior art, on the other hand, the time isdelayed by transfer characteristics Hd as represented by 5 at a positionof the microphone 2. In order to simplify the description, the transfercharacteristics are neglected in the signal processing units such as theadaptive filtering means 6 and the like. By taking the transfercharacteristics Hd into consideration, the control amount calculationunit 84 calculates data to change the period at an early time asrepresented by a curve 4 in the drawing in contrast with the curve 2. InFIG. 6, a change in the period is represented by a straight line withrespect to the time, which, however, may be represented by a curve. Insuch a case, a function is provided for the curve 4 and is found byfitting. In the thus obtained curve 4 of FIG. 6, an estimated period T4is found for the period T3 of the present moment (t₁).

FIG. 8 is a diagram that explains the delay amount control unit, whereinthe delay memory 81 successively receives the input signal data at apredetermined sampling period; the period Tin of the input signals andthe period Tout of the output signals are displayed as being calculatedas tap numbers, and the delay control unit 82 moves the delay point at apredetermined speed V in order to obtain output signals having theperiod Tout from input signals having the period Tin. In FIG. 6, theside A is for explaining the tap speed V that is viewed as an absoluteamount of change. In order to make an input signal period Tin=30 tapsinto an output signal period Tout=29 taps, the taps are moved toward theinput side at a speed of V=1 tap/29 samples. To make Tout=28 taps, thetaps are moved at V=2 taps/28 samples. To make Tout=27 taps, the tapsare moved at V=3 taps/27 samples. To make Tout=15 taps, the taps aremoved at V=15 taps/15 samples. To make Tout=14, the taps are moved atV=16 taps/14 samples. To make an input signal period Tin into an outputsignal period Tout=Tin-n, in general, V should be n/(Tin-n) where n isthe amount of shifting the period.

The side B is to explain the movement of the delay amount control unitthat is viewed as a rate of change. The taps are moved at a speed ofV=1/9 taps/sample to make an input signal period Tin=30 taps into anoutput signal period Tout=(9/10)×30 taps, moved at a speed of V=2/8taps/sample to make Tout=(8/10)×30 taps, - - - , moved at V=5/5taps/sample to make Tout (5/10)×30 taps, and moved at V=6/4 taps/sampleto make Tout=(4/10)×30 taps, - - - . To make an input signal period Tininto an output signal period Tout=(k/10)×Tin, in general, V should be(10-k)/K, where k/10 is a rate of shifting the period.

Next, briefly described below is the adaptive filtering means. Strictlyspeaking, transfer characteristics of electric signals have to be takeninto consideration which, however, have no direct relation to thepresent invention and are not discussed to simplify the description. Thenoise source 1 generates noise S_(N), the transfer characteristics up tothe microphone 2 are denoted by H_(NOISE), the adaptive filtering means6 produces a compensation signal Sc, the transfer characteristics of asystem from the adaptive filtering means 6 to the differential signalcalculation means 5 via the speaker 3 and the microphone 2 are denotedby Hd, and the transfer characteristics of the transfer characteristicssimulation means 4 are denoted by Hdl. Here, if Hdl=Hd, then the signalS_(M) output from the microphone 2 is expressed as S_(M) =S_(N)·H_(NOISE) +Sc·Hd. Therefore, the differential signal S_(E) which is aresult calculated by the differential calculation unit 5, is given byS_(E) =S_(M) -Sc·Hdl=S_(M) -Sc·Hd=S_(N) ·H_(NOISE), i.e., the signal iscalculated when the noise only is detected by the microphone 2. Thedifferential signal S_(E) is input to the adaptive filtering means 6 tocalculate the compensation signal Sc with which S_(M) becomes zero.

FIG. 9 is a diagram illustrating a noise period controller according toa second embodiment of the present invention. What makes theconstitution of FIG. 9 different from that of the first embodiment ofFIG. 2 is that the period-detecting unit 7 does not input signals of adetecting period from the noise source 1 but inputs a differentialsignal fed back from the differential signal calculation means 5; thedifferential signal also being input by the period-adjusting unit 8,because the control amount calculation unit 84 in the period-adjustingunit 8 has the function of predicting a change in the period, and hencethe delay amount control unit 82 reproduces a compensation sound thatcorresponds to a period that is ahead by a delay quantity equivalent tothe transfer characteristics Hd from the output of the period-adjustingunit 8 to the silencing point of the microphone 2 via the speaker 3.

FIG. 10 is a diagram illustrating a noise period controller according toa third embodiment of the present invention. The constitution of FIG. 10is different from that of the first embodiment of FIG. 3 with regard tothe provision of a microphone 105 that directly picks up noise signalsfrom the noise source 1, an amplifier 106 connected to the microphone105, an A/D converter 107 that is connected to the amplifier 106 andforms an input to the period-adjusting unit 8, and a switching unit 108that alternatively selects either one of the outputs from the A/Dconverter 107 or the differential signal calculation means 5 and inputsit to the period-detecting unit 7. That is, the same actions and effectsas those mentioned above are obtained even when the noise signals fromthe noise source 1 are directly input to the period-adjusting unit 8,and either the A/D converter 107 or the differential signal calculationmeans 7 is input to the period-detecting unit 7.

FIG. 11 is a diagram illustrating a noise period controller according toa fourth embodiment of the present invention. The constitution of FIG.11 is different from that of the third embodiment of FIG. 9 in that thetiming signals from the noise source 1 are input to the period-detectingunit 7. This constitution makes it possible to obtain the same actionsand effects as those that were described above.

FIG. 12 is a diagram illustrating a noise sound controller according toa fifth embodiment of the present invention. The constitution of thisdiagram will now be described.

The noise sound controller shown in this diagram comprises a speaker 3for erasing a noise from a noise source 1 such as an engine of anautomobile near a silencing point P (shown in the drawing), an amplifier104 for amplifying the output to the speaker 3, a D/A converter (digitalto analog converter) 103 that converts a digital signal into an analogsignal to feed the analog signal to said amplifier 104, a microphone 2that converts, into an electric signal, the residual sound after noisefrom the noise source 1 is erased by the sound wave from the speaker 3,an amplifier 101 that amplifies the electric signal of the microphone 2,an A/D converter (analog to digital converter) 102 that converts ananalog signal of the amplifier 101 into a digital signal, an adaptivefiltering means 6 that controls the filter coefficient based on a signalfrom the A/D converter 102 and sends a compensation signal for erasingnoise to the speaker 3, a period detect/control means 10 that inputs atiming signal from the noise source 1, inputs a noise signal from amicrophone 105 that will be mentioned later or inputs a noisereproduction signal from a differential signal calculation means 5,detects a noise period, estimates a change in the period, and controlsthe adaptive filtering means 6 depending upon the estimated change inthe period so as to be capable of following a sudden change, amicrophone 105 installed near the noise source 1, an amplifier 106 thatamplifies the output of the microphone 106, an A/D converter 107 thatconverts an analog output signal of the amplifier 106 into a digitalsignal, a transfer characteristics simulation means 4 that is connectedto the output of the adaptive filtering means 6 and simulates transfercharacteristics Hd from the output point thereof up to the input to thedifferential signal calculation means 5, which will be described later,via speaker 3 and microphone 2, a differential signal calculation means5 that calculates a differential signal between the output of thetransfer characteristics simulation means 4 and the output of the A/Dconverter 102, and a switching means 11 that alternatively selects theinput signal of the adaptive filtering means 6. Here, the adaptivefiltering means 6, the period detect/control means 10, etc., areconstituted by DSPs (digital signal processors).

FIG. 13 is a diagram showing the constitution of the perioddetect/control means of FIG. 12. The period detect/control means 10shown in this diagram comprises a period detecting unit 1001, a periodestimating unit 1002, and a control unit 1003 for controllingcoefficients and the like of the adaptive filtering means 6.

FIG. 14 is a diagram explaining a method of detecting the period by theperiod detecting unit of FIG. 13, wherein the diagram (a) is a method ofdetecting an ignition timing or a revolution timing (number ofrevolutions) of an engine or a motor of an automobile that is the noisesource 1. Signals of a rectangular waveform are input to the perioddetecting unit 1001 where a period T thereof is found. The period isthen output to the period estimating unit 1002. A sudden change in thenoise of an automobile is caused by a change in the number ofrevolutions or the like of an automotive engine.

The diagram (b) shows a method according to which, when the timingsignals shown in the diagram (a) are not obtained, a noise waveform isdetected by a microphone or a vibrometer 105 near the engine of theautomobile, and a period T of the noise signals is obtained from peaksin the time waveforms thereof. In this signal processing, a rectangularwave is generated when the level of a noise signal has exceeded apredetermined level, thereby obtaining the period T in the same manneras in the diagram (a).

The diagram (c) explains a BPF (band-pass filter) peak detection methodfor finding a noise period T after a noise signal input to themicrophone is digitized. This method comprises a plurality of band-passfilters 1, 2, - - - , n, absolute value units (ABS) connected to theband-pass filters 1, 2, - - - , n, averaging units (LPF) connected tothe absolute value units, and maximum band-detecting units that detectmaximum values of the averaging units, wherein a maximum frequency bandof the noise level is detected and a period of the maximum frequencyband is used as a period of a noise signal.

The diagram (d) explains a method of detecting the period using anadaptive filter, comprising a delay unit (delay) that inputs adifferential signal S_(R) from the differential signal calculation means8, an adaptive filter (ADF) that inputs the output from the delay unit,an adder unit that obtains a differential signal between the output ofthe adaptive filter and the input signal, and a least-squares processingunit (LMS) that subjects the differential signal of the adder unit tothe method of least squares to determine a coefficient of the adaptivefilter. The period of a noise signal is found from a coefficient of theadaptive filter.

FIG. 15 is a diagram illustrating a method of estimating the amount ofchange in the period based on the detected period. If the period firstremains constant and then decreases starting at a given moment (t₀) asshown in the period estimating unit 1002, the amount of change in theperiod is detected by the period detecting unit 1001 as represented by 1in the drawing. According to the prior art, on the other hand, the timeis delayed by transfer characteristics Hd as represented by 2 in thedrawing at a position of the microphone 2. In order to simplify thedescription, the transfer characteristics are neglected in the signalprocessing units such as adaptive filtering means 6 and the like. Bytaking the transfer characteristics Hd into consideration, the periodestimating unit 1002 calculates data to change the period early asrepresented by a curve 3 in the drawing in contrast with the curve 1. InFIG. 13, a change in the period is represented by a straight line withrespect to the time, which, however, may be represented by a curve. Insuch a case, a function is provided for the curve 3 in the drawing andis found by fitting. In the thus obtained curve 3 of the drawing, anestimated period T₂ is found for the period T₁ of the present moment(t₁). The control unit 103 for controlling coefficients of the ADF andthe like of FIG. 13 will be described later.

The adaptive filtering means 6 will now be briefly described. When thedifferential signal calculation means 5 is selected by the switchingmeans 11, a signal S_(M) of residual sound expressed by S_(M) =S_(N)·H_(noise) +Sc·Hsp is output from the microphone 2 if there holds arelation Hdl=Hsp·Hmic=Hd, where S_(N) denotes noise of the noise source1, H_(NOISE) denotes transfer characteristics up to the microphone 2, Scdenotes a compensation signal of the adaptive filtering means 6, Hspdenotes transfer characteristics of a system from the adaptive filteringmeans 6 to the microphone 2 via the speaker 3, Hmic denotes transfercharacteristics of a system from the microphone 2 to the differentialsignal calculation means 5, and Hdl denotes transfer characteristics ofthe transfer characteristics simulation means 4. Therefore, thedifferential signal S_(R), which is a result calculated by thedifferential calculation unit 5, is given as S_(R) =S_(M)·Hmic-Sc·Hdl=S_(N) ·H_(noise) Hmic+Sc·Hsp·Hmic -Sc·Hsp·Hmic=S_(N)·H_(NOISE) ·Hmic; i e., the signal is calculated when the noise only isdetected by the microphone 2. Moreover, the output S_(E) of the A/Dconverter 102 is given as a control signal for changing the coefficientof the adaptive filter in the adaptive filtering means 6. The adaptivefiltering means 6 so changes the coefficient that the control signalbecomes zero, and S_(M) becomes O when S_(E) =O since S_(E) =S_(M)·Hmic. Therefore, the differential signal S_(R) from the differentialsignal calculation means 5 is input as a signal to be controlled to theadaptive filtering means 6, and the output S_(E) of the A/D converter102 is input as a control signal, so that the adaptive filtering meansso calculates the compensation signal Sc that S_(E) becomes zero. Whenthe microphone 105 is selected by the switching means 11, the adaptivefiltering means 6 calculates the compensation signal Sc upon receiving asignal from the microphone 105.

FIG. 16 is a diagram illustrating the adaptive filtering means that isconstituted by non-cyclic filters. Concretely speaking, the adaptivefiltering means includes a series of delay units 601 that effect thedelay of one sampling period, a plurality of multipliers 602 connectedto the delay units 601, a plurality of adders 603 that add up outputs ofthe multipliers 602, and a coefficient updating means 604 that socontrols the multiplication coefficients of the multipliers 602 that theoutput of the microphone 2 becomes minimal based on the method of leastsquares.

The series of delay units 601 may be constituted by random accessmemories (RAMs). In this case, the sampling data that are input aresuccessively shifted to the next address for each sampling, or thevalues of addresses for inputting the sampling data are successivelyshifted for each sampling.

Described below is how the multiplication coefficients g₁, g₂, - - - ,g_(n) of the multipliers 602 in the adaptive filtering means 6 shown inFIG. 14 are reset by the control unit 1003 in the period detect/controlmeans 10, which controls coefficients of the ADF.

FIG. 17 is a diagram explaining the shifting of multiplicationcoefficients of the plurality of multipliers that constitute theadaptive filtering, wherein the diagram (a) schematically illustratessignals that pass through the delay unit 601. Usually, multiplicationcoefficients (g₁, g₂, - - - , g_(n)) of the multipliers 602 are set bysignals from the microphone 2. When a change from a short period to along period is estimated by the period estimating unit 1002, themultiplication coefficients (g₁, g₂, - - - , g_(n)) of the multiplierunits 602 are shifted into (g'₀, g₁, g₂, - - - , g_(n-1)), - - - ,(g'₋₈, g'₋₇, - - - , g'₀, g₁, g₂, - - - , g_(n-9)) i.e., shifted towardthe n-th multiplier (delay unit) by the control unit 1003, whichcontrols coefficients of the ADF. Therefore, the delay amount increasesand the period can be lengthened.

In the diagram (b) contrary to the above-mentioned case, when a changefrom a long period to a short period is estimated by the periodestimating unit 1002, the multiplication coefficients (g₁, g₂, - - - ,g_(n)) of the multipliers 602 are shifted into (g₂, g₃, - - - , g_(n),g'_(n+1)), - - - , (g₁₀, g₁₁, - - - , g_(n), g'_(n+1), g'_(n+2), - - - ,g'_(n+9)), - - - , i.e., shifted toward the O-th multiplier (delay unit)by the control unit 1003, which controls coefficients of the ADF.Therefore, the delay amount decreases and the period can be shortened.Here, however, g' can be selected to be any optimum value (e.g., 0).

FIG. 18 is a diagram explaining the tap moving of the delay units thatconstitute the adaptive filtering means, which is a modification of FIG.15. In the diagram (a), in general, the taps (T₁, T₂, - - - , T_(n)) ofthe delay units 601 are set. When a change from a short period to a longperiod is estimated by the period estimating unit 1002, however, thetaps (T₁, T₂, - - - , T_(n)) are shifted into (T'₀, T₁, T₂, - - - ,T_(n-1)), - - - , (T'₋₁₀, - - - , T'₋₁, T'₀, T₁, T₂, - - - ,T_(n-9)), - - - , i.e., shifted toward the n-th delay unit by thecontrol unit 1003, which controls coefficients of the ADF. Therefore,the delay amount increases and the period can be lengthened.

In the diagram (b) contrary to the above-mentioned case, when a changefrom a long period to a short period is estimated by the periodestimating unit 1002, the taps (T₁, T₂, - - - , T_(n)) of the delayunits 601 are shifted into (T₂, T₃, - - - , T_(n), T'_(n+1)), - - - ,(T₁₀, T₁₁, - - - , T_(n), T'_(n+1), T'_(n+2), - - - , T'_(n+9)), - - - ,i.e., shifted toward the O-th multiplier by the control unit 1003, whichcontrols coefficients of the ADF. Therefore, the delay amount decreasesand the period can be shortened. Here, however, T' may be any optimumvalue (e.g., 0).

FIG. 19 is a diagram illustrating a modified example of the perioddetect/control means of FIG. 12. The period detecting unit 1001 in theperiod detect/control means 10 inputs the multiplication coefficients ofthe multipliers 602 of the adaptive filtering means 6 and forms thefollowing n-dimensional vector.

    V(t)=g.sub.1 (t)·i.sub.1 +g.sub.2 (t)·i.sub.2 +. . . +g.sub.n (t)·i.sub.n

The adaptive filtering means 4 successively updates the multiplicationcoefficients (g₁, g₂, - - - , g_(n)) as shown in the diagrams (a), (b)and (c), and the period estimation unit 1002 traces the vector like t=0,1, 2, - - - to estimate the vector after a time t. Based on thisestimation, multiplication coefficients (g₁, g₂, - - - , g_(n)) arefound from the vector and are set to the multipliers 602 by the controlunit 1003, which controls coefficients of the ADF. Thus, the filteringcharacteristics of the adaptive filtering means 6 can be changed bychanging the multiplication coefficients of the multipliers 602 that areincluded in the adaptive filtering means 6 or by moving the output tapsof the delay units 601.

According to the present invention as described above, a noise period ofa noise source is detected and the period is controlled in an estimatedmanner based on the characteristics of the noise period. Therefore, evena sudden change in frequency can be followed.

INDUSTRIAL APPLICABILITY

The present invention can be advantageously applied to a digital signalprocessor for canceling a noise sound of engines, motors and the like.

I claim:
 1. A noise sound controller outputting a compensation sound tocancel a noise sound generated from a noise source, the compensationsound having a phase opposite to a phase of the noise sound and a soundpressure equal to a sound pressure of the noise sound, the noise soundcontroller comprising:sound wave-electric signal means for trapping,near a silencing point, a residual sound remaining after canceling thenoise sound with the compensation sound and for converting the residualsound into an electrical signal as an error signal; electricsignal-sound wave means for outputting said compensation sound; adaptivefiltering means for updating a plurality of filter coefficients and forobtaining said compensation sound based on said error signal, saidadaptive filtering means outputting a compensation signal; transfercharacteristics simulation means provided at an output of said adaptivefiltering means for simulating transfer characteristics of a system froman output of said adaptive filtering means to a point returning as saiderror signal passing through said electric signal-sound wave means andsaid sound wave-electric signal means; differential signal calculationmeans for calculating a differential signal between the compensationsignal output from said adaptive filtering means through said transfercharacteristics simulation means and said error signal from said soundwave-electric signal means, said differential signal calculation meansoutputting a reproduction noise signal; period-detecting means formeasuring a noise period of the noise source; and period-adjusting meansfor varying a delay period of an output signal from said differentialsignal calculation means depending upon an amount of change of saidnoise period.
 2. The noise sound controller of claim 1, wherein saidperiod-detecting means detects the noise period from the reproductionnoise signal of said differential signal calculation means.
 3. A noisesound controller outputting a compensation sound to cancel a noise soundgenerated from a noise source, the compensation sound having a phaseopposite to a phase of a noise sound and a sound pressure equal to asound pressure of the noise sound, the noise sound controllercomprising:sound wave-electric signal means for trapping, near asilencing point, a residual sound remaining after canceling the noisesound with the compensation sound and for converting the residual soundinto an electrical signal as an error signal; electric signal-sound wavemeans for outputting said compensation sound; adaptive filtering meansfor updating a plurality of filter coefficients and for obtaining saidcompensation sound based on said error signal, the adaptive filteringmeans outputting a compensation signal; first period detecting/controlmeans for measuring a noise period of said noise source, for estimatinga change in the noise period, and for changing the plurality of filtercharacteristics of said adaptive filtering means depending on theestimated change in the noise period, the first period detecting/controlmeans including: period detecting means for measuring the noise periodof said noise source, period estimating means for estimating a suddenchange in the noise period; and second control means for lengthening thenoise period when a change from a short period to a long period isestimated by the period estimating means and for shortening the noiseperiod when a change from the long period to the short period isestimated by the period estimating means.
 4. The noise sound controllerof claim 3, wherein said second control means controls the plurality offilter coefficients of said adaptive filtering means, the control meansincreasing a delay amount in response to the period estimating meansestimating the change from the short period to the long period anddecreasing the delay amount in response to the period estimating meansestimating the change from the long period to the short period.
 5. Thenoise sound controller of claim 3, wherein said first perioddetecting/controlling means measures the noise period of said noisesource, estimates a change of the noise period, and moves a plurality ofoutput taps of a plurality of delay units included in said adaptivefiltering means depending on the estimated change in the noise period.6. The noise sound controller of claim 3, wherein said first perioddetecting/controlling means forms a vector of a plurality of dimensions,detects a change in the vector, estimates the change in the vector, andsets a multiplication coefficient of a plurality of multipliers includedin said adaptive filtering means in response to the detected change inthe vector.